1. Field of the Invention
The present invention relates to an optical pick-up actuator and more particularly to an optical pick-up actuator operable in multiple axes.
2. Background of the Related Art
Generally, an optical pick-up actuator plays a role of maintaining constant relative position between an object lens and an optical recording medium (e.g. a disk) by moving elements (bobbin, lens holder, etc.) including an object lens. Also, the optical pick-up actuator plays a role of recording information and playing recorded information by tracing a track of an optical recording medium.
FIG. 1 is a view of a structure for an optical pick-up actuator of a related art.
Referring to FIG. 1, the optical pick-up actuator of a related art is of a structure such that an object lens 101 is mounted on a lens holder 102, a focusing coil 105 for performing focusing being attached on a periphery of the lens holder 102, a tracking coil 106 wired in an appropriate direction, for performing tracking being attached on each corner section.
Also, a permanent magnet 103 is fixed on the inner surface of a U-shaped yoke 104 which is a member of ferromagnetic material positioned on right and left of the lens holder 102, and the yoke 104 is integrally formed together with a pick-up base (not shown) by integrating means.
A fixing unit 108 is joined to the central part on the lateral side of the upper and the lower part of such lens holder 102, one end of two parallel wire suspensions 107 being fixed in each of the fixing units 108, and the other end of the wire suspension 107 being fixed in a main PCB 111 through a frame 109 located on one side of the lens holder 102.
Here, a damper (not shown) is joined in the inside of the frame 109 so that the wire suspension 107 having rigid property may have attenuation characteristics and a main PCB (not shown) is joined in the outside of the frame so that the other end of the wire suspension 107 maybe fixed in a soldering manner.
Such wire suspension 107 raises the lens holder 102, playing a role of supplying a current as a relay line.
Operation of the actuator having the foregoing construction will be described in the following. As shown in FIG. 1 and FIG. 2, a focusing coil 105 is wired in vertical direction unlike a tracking coil, so that magnetic flux is generated in up and down direction upon flowing of a current i, interacting with magnetic flux of a fixed magnet 103, whereby force is generated, in vertical direction, at the focusing coil 105. Thanks to such vertical force, the lens holder 102 is moved in a focusing direction (vertically up and down) and a focusing servo operates for correcting a focusing error.
The tracking coils 106 attached on the lens holder 102 are appropriately wired each other, for generating magnetic flux in a predetermined direction upon flowing of a current, interacting with magnetic force of the fixed magnet 103, whereby repulsive force is generated. Thanks to such repulsive force, the lens holder 102 is moved in tracking direction (right and left), whereby a tracking servo operates for correcting a tracking error.
A type such that the coils 105 and 106 are wired on the outer periphety of the lens holder 102 and moved in the tracking and the focusing directions together with the lens holder 102, is referred to as a moving coil type. On the contrary, a type such that a magnet is attached on the outer periphery of the lens holder 102 and moved together with the lens holder 102, is referred to as a moving magnet type. At the moment, movement types by the magnet and the coil make use of Lorenz force by Fleming's left-hand rule.
Such optical pick-up actuator 100 moves using coils operable by magnetic field of permanent magnet, whereby an object lens is moved to a predetermined desired position on an optical recording medium. At the moment, the lens holder, which is a moving part of the optical pick-up actuator, is fixed by the wire suspension having rigid property and attenuation characteristics, so that a predetermined frequency characteristics is provided. Also, the lens holder performs a translational motion in the focusing and the tracking directions which are two mutually perpendicular directions, and motion should be performed without unnecessary vibration such as rotation and twisting.
But, in the structure as shown in FIG. 1, sufficient control for reading and writing recorded information could not be made in response to a disk of high density. Namely, as capacity of a disk increases, data recorded per unit length of a track formed on a disk increases, and a number of tracks themselves formed on a disk increases.
In a record density of a general disk, a width of a track itself and an interval between tracks are useful so that data could be sequentially and sufficiently accessed by only movements of the pick-up itself and the lens of the actuator, but in a disk format of high density, data could not be exactly accessed by the actuator of a related art.
To resolve such problems, as shown in FIG. 3, a tilt component needs to be corrected so that a laser beam reflected through the reflecting mirror 112 may be exactly projected to a reflection plane of an optical disk 110 by an object lens 101.
But, to correct a tilt component according to movement of the lens holder 102, the actuator should operate in a tilting motion mode in a radial direction as well as the translational motions in the tracking and the focusing directions. According to the related art structure, however, operation in the tilting motion mode is not possible.